Portable electronic devices and wireless telecommunication devices such as mobile telephones and pagers typically include vibrators for quietly signaling an event such as an alarm or that a call has been received. If the portable electronic device is touching the user or is in close proximity to the user, the user will hear or feel the vibration and will know that an event has occurred or that a call is being received.
FIGS. 7 and 8 show a typical vibrator 705 for a wireless communication device 704. A motor 700 is held by a motor bracket 706 within a housing of the wireless communication device, and the motor bracket 706 is fixed to a printed circuit board 712. An eccentric weight 708 is fixed to a metal motor shaft 702 in an eccentric position. That is, the center of gravity 718 of the eccentric weight 708 is offset from the axis of the motor shaft 702. When the motor 700 rotates the eccentric weight 708, vibration is created, which is transmitted to the housing of the wireless communication device 704.
If the wireless communication device 704 is dropped, the motor shaft 702 may be permanently bent due to an inertial force applied to the motor shaft 702 by the eccentric weight 708. For example, if the portable electronic device 704 is dropped such that a generally flat surface of a first housing member 714 strikes a hard surface, an impact force 720 is applied to the housing and a great amount of stress may be applied to the motor shaft 702, which may cause the motor shaft 702 to permanently deform, due to the inertia of the eccentric weight 708. If the motor shaft 702 deforms permanently, there is a good chance that the vibrator will be disabled or will generate noise due to interference between the eccentric weight 708 and other parts in the housing.
Typically, the motor 700 is oriented such that the axis of the motor shaft 702 is parallel to a planar or generally planar external housing member 716, 714. Thus, the risk of permanent deformation of the motor shaft 702 is particularly great when the portable electronic device 704 falls such that the axis of the motor shaft 702 is parallel to the ground when the portable electronic device 704 strikes the ground. That is, if the motor shaft 702 is parallel to the ground when the portable electronic device 704 strikes the ground, the force of impact 720 is perpendicular to the motor shaft 702, and the resulting stress on the motor shaft 702 is maximized as compared to other motor shaft orientations.
Furthermore, the risk of permanent deformation of the motor shaft 702 is greater when the center of gravity 718 of the eccentric weight 708 is located on an opposite side of the axis of the motor shaft 702 from the point of impact at which the housing strikes the ground. That is, when the axis of the motor shaft 702 is directly between the center of gravity 718 of the eccentric weight 708 and the point of impact, then inertial force that the eccentric weight 708 applies to the motor shaft 702 is applied directly to the motor shaft 702 and maximizes the stress on the motor shaft 702. Thus, FIGS. 7 and 8 represent an orientation of the eccentric weight 708 and the axis in which the risk of permanent deformation of the motor shaft 702 is the greatest, since the axis of the motor shaft 702 is between the center of gravity 718 and the point of application of an impact force 720, and the impact force is perpendicular to the axis of the shaft. Thus, under the conditions of FIGS. 7 and 8, the motor shaft 702 will deform in the downward direction of the figures as a result of the impact force 720, and permanent deformation of the motor shaft 702 may result.